Bacteriophage T4 RNA ligase will be studied by a combined enzymological and genetic approach. To explore the physiological role of the enzyme, we will attempt to find an activity of the enzyme in nucleic acid metabolism. The two approaches will be the construction of double mutants in gene 63 to minimize active gene 63 product and the determination of the inability of non-lethal gene 63 mutants to grow in a DNA ligase-, rII background. To develop the enzyme as a tool for synthesis of nucleic acids we will refine the reaction conditions for intermolecular joining single-stranded DNA.